A ring of anti-prisms
A ring can
be made of thirteen square anti-prisms. It
is however, not quite regular. It can be shown that to complete
the toroid takes approximately 13.01 square anti-prisms. It's a nice
near miss though, and a physical model shows no visible distortion
(stress map - cones
exaggerated x 100). Distortion
(E=0.041, P=0 , A=5.5°). It's not the closest such near miss; eighty-three icosikaitetragonal (24-gonal) antiprisms can be formed
into a ring with an error of only 1/7700th of an anti-prism.
Thanks to Charles Butler for bringing the above near miss to my attention.